The present invention disclosed herein relates to a wireless power transmission system, and more particularly, to a wireless power transmission device, a wireless power reception device and a wireless power transmission system that identify the charged state of a secondary cell.
There are roughly three wireless energy transmission techniques. Firstly, there is a technique of transmitting power by using electromagnetic induction, secondly, there is a technique of transmitting power by using radio frequency, and thirdly, there is a technique of transmitting power by using an ultrasonic wave.
Firstly, a wireless power transmission system using electromagnetic induction includes a body generating charging power by using external power, and a power reception module receiving charging power from the body through electromagnetic induction. The electromagnetic induction has high efficiency and is closest to commercialization.
Secondly, the wireless power transmission system using RF collects RF energy that has a very long propagation distance, and supplies power to an electronic device or a sensor. There are many RFs in the air and they have an advantage in that their propagation distances are very long.
Thirdly, the wireless power transmission system using an ultrasonic wave includes a transmission device that generates an ultrasonic wave, and a reception device that receives a generated ultrasonic wave. Vibration generated from an ultrasonic device vibrates a medium by interaction with the medium and the ultrasonic wave is transmitted through a vibrating medium. Recently, a system that charges a battery by using such an ultrasonic wave generator has been disclosed.
However, the above-described wireless power transmission system has a limitation in that unnecessary power is transmitted to a secondary cell because the charged state of the secondary cell is not accurately identified.